


one-up

by daisylincs



Series: Agents of Birthdays [23]
Category: Agents of S.H.I.E.L.D. (TV)
Genre: Agents of Birthdays, Alternate Universe - Corporate, Alternate Universe - No SHIELD (Marvel), Arguing, Bickering, Eventual Happy Ending, F/M, Fake/Pretend Relationship, FitzSimmons - Freeform, Gift Fic, Happy Birthday Libby!!, Idiots in Love, Implied/Referenced Sex, Mutual Pining, Office Rivalry, Rivals to Lovers, being the two smartest people in the room, birthday fic, scientific rivalry, the author knows nothing about science but enjoyed using big words to make herself sound smart
Language: English
Status: Completed
Published: 2021-02-22
Updated: 2021-02-22
Packaged: 2021-03-12 20:48:10
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 9,088
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29640456
Author URL: https://archiveofourown.org/users/daisylincs/pseuds/daisylincs
Summary: Dr Jemma Simmons is something of a pioneer in her field. A genius, really. Unfortunately, though, all the men she works with are either total idiots, or far more interested than getting into her knickers than in getting into her brain.Then she meets the one exception to the rule - not only is Dr Fitz just as brilliant as she is, but he's also the first man she really wouldn't mind sleeping with.Too bad they hate each other’s guts.
Relationships: Leo Fitz/Jemma Simmons
Series: Agents of Birthdays [23]
Series URL: https://archiveofourown.org/series/1886911
Comments: 10
Kudos: 37





	one-up

**Author's Note:**

  * For [LibbyWeasley](https://archiveofourown.org/users/LibbyWeasley/gifts).



> Dear Libby,
> 
> Oh, my goodness, happy birthday - happy birthday to one of the kindest, most wonderfully supportive and just most 'amazing' fandom people in general! You really are right up there among the very best when it comes to friendship and dedication, and I think that a comparison to one Jemma Simmons wouldn't be unrealistic. In fact, I think it would be _wholly_ warranted! You really do remind me of her - warm, and kind, and absolutely _wonderful,_ from top to bottom. 
> 
> And as though that all isn't enough, you're also one of _the_ most talented writers in this fandom! You know, I can still remember the first time the two of us properly met so well - it was very shortly after my official entry into the AoS fandom, and I had just found and positively _devoured_ your Just Friends series. I remember thinking, "well, if everyone in the fandom is this talented, I'm in for a real treat!" 
> 
> Then your _replies,_ oh, your replies. At that point, I was still pretty darn shy online, and absolutely terrified of anything involving the word "author," especially interacting with people like you whom I admired so much - but, gosh, you just made it so _easy._ Your replies to those early comments were like nothing more than _warm hugs_ , and I found myself absolutely bowled over and SO touched by the warmth of your welcome. 
> 
> And then you continued on to unfailingly support _me_ when I finally started to gather the courage to post my own stuff - and what's absolutely freaking INCREDIBLE is that you've kept doing that to this very day. No matter what, you have a kind word and a supportive ❤️ to deal out - and, honestly, I do not have enough words in this English lexicon to describe how special that is. You're just one of those people one can trust and rely on completely, and, Libby, I appreciate you so, so, _so_ much. 
> 
> Thank you, from the bottom of my heart _thank you,_ for all the amazing things you did for me, and so many other people in this fandom - and keep doing to this day. You truly are one of the people I admire the most in this entire internet world, and I am SO lucky to be able to consider myself as one of your friends.
> 
> And with my very warmest, Fitzsimmonsy-est hugs today - HAPPY BIRTHDAY, Libby!!!!! 🎂🎉❤️

"Ms Simmons?" 

The voice was leering, and patronising, and _all_ too familiar, and Jemma squeezed her eyes shut for a moment before spinning her chair around, forcing a polite smile she didn't feel at _all_ to her lips. "It's _Dr_ Simmons, actually," she said, proud of herself for managing to refrain from adding a snide, _as I've told you at least seventeen times this week alone._

Donald Bryson, her co-worker and probably the biggest arsehole she had ever had the misfortune of meeting in the corporate science business, waved a hand and made a lazy, drawling kind of an unconcerned snort. "Yeah, yeah, titles, titles," he said, leaning his elbows on the back of her chair. His breath, slightly and regrettably scented by stale Cheetos, was hot and panting on the back of her neck. 

"Titles," he repeated, and Jemma cringed internally, hoping against hope that she wouldn't find little specks of orange dust in her hair this evening. "Ya know I don't like things to be so formal between us, doll." 

Stiffly, Jemma pulled her chair forward, rearranging the papers on her desk and shutting a file with a sharp, satisfying _snap_. "Did you require my assistance, _Dr_ Bryson?" 

"Call me Don," he said, his drawling accent stretching the nickname out to almost twice its length, which, Jemma thought drily, rather ruined the point of a nickname in the first place. 

Bryson was looking at her with hooded eyes and a smirk that just _oozed_ lecherous, leering confidence, unashamedly staring at the patch of skin below her collarbone that her crisp, professional blazer still left bare. He dragged his gaze back up to hers, smirking, and watching her with this expectant expression like he was God's gift to women and just waiting for her to fall all over him. 

Jemma stood up and shoved her chair back, feeling a quick, vicious burst of satisfaction at Bryson's pained yelp. _"Doctor Bryson,"_ she repeated, doubly emphasizing each crisp syllable. "Unless you have an urgent issue that needs my immediate attention, I'm afraid my expertise is needed elsewhere." 

Bryson scrambled after her, rubbing his leg where her chair had hit him. "There's no need to be like that, doll," he said in a smarmy, parlaying tone, reaching for her wrist. 

Jemma yanked her arm away, redoubling her pace to the line of printers on the opposite side of the office. "Thank you for your time, Dr Bryson," she said crisply. 

Bryson was running after her for real now. "Doll, wait, wait, wait. The boss wants you in conference room five." 

Biting back the urge to snap out something along the lines of, "well, you could've just led with that," Jemma gave him a quick, civil nod. "Thank you," she said, changing course to head in the direction of the conference rooms. 

"I'll be in the bar from seven PM, waiting just for you!" Bryson called after her, and Jemma pretended not to hear him as she stepped into the elevator and hit the Up button with a probably unnecessary amount of force. 

She blew out a long, long breath once the doors slid shut, screwing up her face and making a furious little growling sound. 

_Why_ were all the men in her field such absolute idiots? _None_ of them appreciated her for her intelligence, not a _single_ one. 

And all of that while she was easily the smartest person in this entire bloody company… 

But when the elevator doors slid open with a pleasant _ding,_ there was no sign of her indignant fury anywhere on her face, or in the pleasant smile she gave to the group of men waiting to get in on the other side _(all_ of whom, she had to notice, glanced at her chest well before they looked up at her face.) 

"Dr Simmons!" a new voice exclaimed, sounding surprised to see her even though he was the one who had called her up. 

“Dr Mace,” she replied politely, her heels clicking against the tiled floor as she made her way over to them, ignoring the gaggle of staring men. 

Mace smiled at her in a patronising, fatherly sort of fashion, and she could almost _feel_ the waves of rampant patriotism rolling off him. “Right this way, right this way,” he said, gesturing at the conference room behind him with a sweeping arc, as though she wasn’t capable of reading the large label _5_ above the door.

“We’re getting a new consultant for the engineering department today,” Mace told her, passing her a thick stack of folders. “We’re going to need you to brief him on how he can help us out as effectively as possible.” 

His constant use of _we_ \- like he had _ever_ spent a single day in a lab with her or any of the idiots on her team, _come on_ \- was really starting to grate on her nerves. 

“Remember,” he said, completely oblivious to her irritation as he beamed down at her in what he obviously thought was an inspiring fashion, holding the door open for her. “A team that trusts -” 

“- is a team that triumphs. Yes, sir,” Jemma finished for him, squeezing past him and into the conference room before he could launch into the rest of his “motivational” lecture. 

Yeah, Mace’s MO was all about trusting and teams - nowhere, she had to note, did it mention _talent._

In all the years she had worked for him - and, what, it had to be almost approaching five now - she had never _once_ encountered another halfway-decent scientist.

Actually, that wasn’t quite true. There had been this _one_ guy, Martin Something-Or-Other, and he had had a pretty quick mind, she had to grant him that - but he had always been way, way, _way_ more interested in talking about her _attractiveness_ than in talking about her _projects._

 _Their_ projects, actually - which meant the whole thing had ended up about as well as you would imagine. 

Case in point, though, Jemma did _not_ have very high hopes for this new consultant of Mace’s, particularly not when she entered the conference room and saw him reading over a stack of files similar to her own with a heavy frown.

Internally, she heaved a long, deep sigh. Another dummy who would need her to explain the inner workings of their project from the very basics, and who she’d have to put on a pretty act for as though she didn’t know his own subject better than he did.

Clearing her throat politely, she set her stack of files down on the large table and offered the friendliest smile she could muster. “Good morning,” she said pleasantly. “Is there something I can help you to understand?” 

The man glanced up, stepping slightly forwards and out of the back-lighting of the large window that had been mostly hiding his features from her. Jemma’s mouth went a little dry. 

_Whoa._

Bright blue eyes, sandy curls, and a crisp, fitted grey suit… Whoever this man was, he was one of the most attractive specimens she had _ever_ laid eyes on.

… Which was, of course, _wholly_ unprofessional of her, especially considering that said attractive man was actually speaking to her!

Jemma gave herself a sharp mental shake, feeling disappointed and a little disgusted in herself. She was _not_ one of those cliché girls who lost their minds completely at the first glimpse of an attractive man, thank you _very_ much. 

(She wasn’t denying that this man was very, very, _very_ attractive though… just, _whoa._

But that really wasn’t the point here.) 

Forcing herself to tune in to what the man was saying, Jemma pushed all thoughts of his aesthetic appeal to the very _back_ of her mind. 

“... know who wrote this piece?” he was asking, and the indignant tone of his voice caught her by surprise.

“Why, yes, I believe I do,” she said, feeling strangely defensive all of a sudden. 

The man’s oh-so-bright blue eyes flashed, and he threw up his hands in an exasperated gesture. _“Good!_ Because I need you to ask them why the _bloody hell_ they used a Runge-Katta integrator in the navigatory fuse?” 

Jemma had to fight hard against the urge to roll her eyes. Why was her luck _always_ this bad? Though attractive, this man was obviously a complete _ninny_ \- hadn’t he _studied_ that these integrators were used for the temporal discretization of the system’s differentials? 

While she appreciated his considerate use of the neutral “they” pronoun - it was _rare_ to find a man who didn’t immediately assume any authoritative paper was written by another man, especially in a field such as engineering - but that and his physical appeal were clearly this man’s _only_ redeeming qualities.

His brain? _Nothing_ to write home about, _whatsoever._

As always…

Using her long-suffering, patient voice, Jemma began to explain, “Well, you see, for effective gathering of the LIDAR data, the system’s differentials need to -” 

“Undergo temporal discretization, yes, I _know_ that,” the man cut her off, waving an impatient hand. _“Obviously._ My question is - why use a Runge-Katta integrator in place of a matrix Lie group integrator?” 

Jemma’s jaw _dropped,_ and for a long second, her brain blanked completely except for one phrase, which repeated itself over and over and over again in an endless, drumming refrain - _he knows what he’s doing._

“B...but that would interfere with the sensor fusion with the inertial measurement unit,” she found herself saying faintly, her brain still scrambling to process the fact that _this was a man who not only knew what he was talking about, but was_ here _and knew what he was talking about. Right now._

“Right, but you could get rid of that flaw by simply inserting a basic metamaterial with several repeating units,” this unbelievable man shot back, so quick on the uptake that it left Jemma reeling. _“Besides,_ using a matrix Lie group integrator would allow the developer to code in a cascaded sigma point Kalman filter, as well.” 

Jemma shook her head slowly, her mind racing through the coding and projecting the calculations as best she could. “I don’t…” she said, and trailed off into a weak silence, most of her brain still refusing to process that _this was really happening._

“You do know what a sigma point filter does, don’t you?” The man was impatient now, gesturing sharply with his hands. “It’s a probabilistic framework for the non-linear estimation of -” 

“I know what a cascaded sigma point filter is,” Jemma snapped, cutting him off mid-explanation. “I just don’t see how you could integrate it into the -” 

_“With a matrix Lie group integrator,”_ the man said, with all the impatient aplomb of a professor delivering a lecture he knew his students wouldn’t understand.

Jemma shook her head once, then again, harder. She didn’t see how it could be… but then again, if you re-coded the navigational differential… linking the fused sensors with the matrix Lie integrator… 

Shut the _front door,_ he was right.

This man, whoever he was, was _right._ He was completely and absolutely right. 

Jemma couldn’t _believe_ she hadn’t seen this before! Using a matrix Lie group integrator made the whole process _so_ much faster, and about twenty times more accurate as well -

“... and so _obviously,”_ the man was saying now, his face twisted in an impatient grimace that Jemma recognised all too well from her own face when dealing with a particularly inferior teammate, “whoever came up with this sorry excuse for a blueprint obviously knew _nothing_ about their field.” 

_That_ got Jemma’s brain fully back online. _“Excuse_ me?” she spluttered.

The man spared her an impatient glance, then turned back to Mace, who in fact he had just been addressing. “Rubbish,” he said matter-of-factly, and then he actually had the temerity to _rip the blueprint in two._

And that was _her_ blueprint. 

Now, Jemma wasn’t the kind of person who believed in anything at first sight, but she was most _certainly_ re-evaluating her initial good impression of this man. Sure, he was right, she had made a mistake, but it wasn’t like it was _that_ stupid. Her supposed team came up with shittier designs on a daily basis!

No, he was _way_ out of line, and it was making her see red.

What the hell gave him the right to be this hateful, anyway? 

Stepping forward so sharply that she almost twisted her high heel beneath her, she ripped the shreds of the blueprint out of the man’s hands. _“Thank_ you,” she said, and she didn’t think she had ever heard her voice sound colder, “for your suggestions. I will keep them closely in consideration.” 

Then she turned and stormed out of the conference room, blatantly ignoring Mace’s call for her to wait.

She might not even know this man’s name, but she had never hated anyone more. 

How _dare_ he humiliate her this badly, with no provocation? 

Yes, she had been working under the crappiest team on the planet, with probably the worst boss and the most tragic waste of her potential imaginable, but she hadn’t thought it would make her _this_ behind on what was actually going on in the competent scientific world. 

She had become so used to working with the most useless dregs of the scientific sewer that she had lost all sense of challenge, and in consequence stopped challenging _herself_ to find the most effective, innovative solutions possible. In short: anything she did would already be so many leagues above what the rest of her team could drum up, so why should she really exert herself to try?

In short, she had _failed._

And, _well._ If there was one thing about Jemma Anne Simmons that was an up-and-down _fact,_ it was this - _she was not a failure._ Now, or ever. 

Still vibrating with anger, she slammed the two halves of the blueprint down on her desk, narrowing her eyes in the direction of the engineering section. 

Oh, she was going to _show_ him. 

//

The man - his name, she learned, was _Dr Leopold Fitz_ \- tried to catch her on her lunch break, but she turned her back and slammed the fridge door so pointedly that he got the message.

No, thank you _very_ much, she didn’t want to hear another one of her projects ripped apart. 

What she _did_ want to do, though? 

Rip apart one of _his_ projects. Make him feel that exact same jolt of shock, disbelief, dismay, and burning humiliation that had nailed her to the spot in that conference room. 

He thought he was so smart, and quick on the uptake, and more intelligent and well-informed than everyone else in the room? Oh-ho- _ho,_ she was going to show him.

And as the department head for biochem, she happened to know when he would be holding the presentation for his new-and-improved, no-doubt-featuring-a-matrix-Lie-group-integrator blueprint design.

And as the department head for biochem, she just _happened_ to have to be in attendance at said presentation.

She planned to make _quite_ the mark.

She stayed up till two, three AM at night, _easily,_ and though there were rings under her eyes and a fuzzy, tired buzzing in her head at strange times, she couldn’t remember the last time she had felt this _alive._ Her mind felt vibrant, strong, _inspired_ \- she had a goal, and she had a clear plan for how to achieve it, set out step-by-step with research notes.

He thought a matrix Lie integrator was such a revolutionary change? Well, she was going to find every _single_ flaw in its design, and pick it apart to the very _bone_ in that presentation. She was going to make him regret the day the words “matrix Lie integrator” had come out of his mouth. 

The day dawned bright and sunny (one of the few advantages she had to grant to America, California specifically, above home - it rarely, _rarely_ rained, and she didn’t think she had woken up to a dreary grey sky _once_ since moving here.) But yes, with the golden-bright sunshine shining down on her, and the low, automated hum of cars on the highway in the distance, Jemma felt _powerful._

She felt ready.

Was Fitz? 

She thought, _no way in the actual bloody_ hell _is he ready for it,_ and it made a primal, bone-deep satisfaction curl in her belly. 

She managed to keep a pleasant smile on her face for the entirety of the morning, though, even succeeding in enduring Bryson’s ever-unwelcome attentions without grimacing too much.

And when two o’clock rolled around, she was in the conference room - ah, the same conference room from a week ago, it felt like karma - still maintaining her friendly smile even as Dr Fitz himself walked in. 

He was brusque and to-the-point, clicking his tablet to activate his presentation and launching straight in without wasting their time on a dilly-dallying introduction. “I’m here to give you all the specs of the new LIDAR-data gathering and transforming self-powered, fully autonomous hoverdrone,” he said crisply, and promptly launched into a concise, detailed description of exactly what his design entailed.

Jemma let him speak, smiling to herself. This useless team of hers could look as impressed as they wanted - they were in for a _real_ show soon. 

“- by making use of a matrix Lie group integrator,” Fitz said, pausing for a moment to draw breath as he pulled up the relevant slide behind him.

Jemma coughed gently.

Fitz glanced up, narrowing his eyes as he looked around the room, but not noticing anything immediately out of place. “A matrix Lie group integrator,” he tried to start up again. 

But Jemma coughed again, a little louder this time. 

Nostrils flaring impatiently, Fitz looked around the room again - this time locking onto her as the guilty party. 

“Did you have a question, Dr Simmons?” he asked, his voice heavy with irony - but Jemma thought that she might have detected just the faintest hint of apprehension in his eyes. 

There was something else too, something softer and guiltier, but that was _not_ what she was here for this afternoon. Apprehension? Hell yes, that was exactly the plan. 

Jemma lowered her head, faking embarrassment and looking up at him through her lashes with her most angelic smile. “Yes, I do, actually,” she said innocently. “I was wondering why you feel the need to use a matrix Lie integrator?” 

Acute disbelief flashed in Fitz’s blue eyes, and for a second she thought that he was going to explode. 

On some level, she sympathised with the feeling. Having to explain the same thing over and over again to a complete moron was the most frustrating feeling in the _world._

 _But we all have to do things we don’t like sometimes, don’t we?_ Jemma thought, feeling like a cat who had just caught the canary. 

“The matrix Lie integrator,” Dr Fitz explained in a tone of very strained patience, “allows the system to perform temporal discretization on the differential LIDAR data it gathers - at twice the usual speed, and with triple the accuracy of a Runge-Katta integrator, I might add.” 

That last bit was pure jibe, but Jemma just smiled through it, feeling wholly shark-like as she said, still in that polite, pleasant, even tone - “Oh, I agree, Dr Fitz. I was just wondering what the numbers might look like if you used a _variational_ integrator instead.” 

She saw the exact moment the realisation hit - saw the impatient frustration freeze on his face, saw some of the colour drain from his cheeks, pinpointed the exact moment he finished running an estimate of a simulation in his head.

His eyes said, oh, _shit,_ and Jemma’s entire being _sang._

“As I’m sure you know,” she said, her voice syrupy-sweet, “a variational integrator has the same efficacy rate as a matrix Lie group integrator, but without the interference to the fused sensor system. That would allow the developer to -” 

“- eliminate the use of the metamaterial repeat units,” Fitz breathed, looking simultaneously shell-shocked and utterly horrified - at _himself._

Though that expression was making some primal part of her want to shriek and punch the air, Jemma kept her cool, continuing calmly on, “And that, of course, would allow for a fifth of the additional weight to be shaved off, providing a reduced production cost.” 

Fitz shook his head, and blinked. Then blinked again. “But you’d have to sacrifice some systematic accuracy to do it,” he said, his voice faint and disbelieving.

Again, Jemma knew that feeling _all_ too well, but again, she refused to let her triumph overcome her. “Maybe so, but you could make up for it by coupling the differential unit to create a discrete Lagranian.” 

The second shock of the afternoon hit Fitz, and it hit hard. “That…” he stammered, and then swallowed, his throat bobbing in what Jemma noticed with delight seemed to be genuine shock. 

And dismay. _Lots_ of dismay, naturally. 

_All_ aimed at himself.

Oh, she was enjoying this far too much.

Pinching the bridge of his nose, Fitz pulled out an Apple pencil, beginning to sketch out the equations for the new system differentials.

His face was bereft of all colour, though, and if Jemma had to guess, he was having the same trouble thinking clearly that she had exactly a week ago.

It was the shock, doubtless. Neither of them were used to being blown away by someone _so_ competent. 

As far as Fitz went, though, Jemma was _far_ from done. This man could still be blown away further.

So, still keeping her pleasant smile on her face, she crossed the room and blatantly pulled the tablet and Apple pencil out of his hands, finishing the equation for him in a few quick, decisive movements. 

She handed him back his tablet, making sure to tilt the screen so that he could see exactly what she had written. 

“I’ll be expecting a full progress report on your project updates in a week’s time,” she said, her voice sweeter than honey.

 _Then_ she turned on her heel and marched out of the conference room.

And this time, as she did so, Jemma felt nothing but utter triumph. 

//

By the next day, the story of their little spat had circulated all through the office, and Jemma was greeted by a long round of wolf-whistles when she walked in the next day.

She just rolled her eyes and ignored them, because, wolf-whistles, _really?_ What was that even supposed to mean? _Congrats, you got a point over the guy who completely trashed you a week ago?_

Yeah, no. She didn’t have any interest in their opinions and approval. 

What _did_ interest her, though, was the glint she saw in Dr Fitz’s bright blue eyes when he nodded at her from across the office. Surficially, there was nothing wrong with the nod - it was a perfectly acceptable _good-morning-coworker_ type of nod, polite and superficial.

But his eyes… _oh,_ Jemma recognised that expression. It was exactly how she had looked in the mirror every single day for the past week. 

_Planning. Thinking. Challenging._

She knew he was going to try and equalise in their next meeting. He _had_ to. She had given him a full-on blow to the pride.

Well, that was all very good for him, he was _welcome_ to do all the prep work he wanted.

She, however, was doing the exact same thing.

There was just no _way_ she would let him get another one over her. Ohhh, _hell_ no. She would cover every _possible_ argument he could make, and come up with a stronger, fact-based counterargument.

She was so focused on _succeeding_ in setting up said counterargument that she barely even noticed when another week passed. The rote forms and boring, predictable experiments Mace asked her to perform and analyse? Whatever. She barely even paid them any heed, getting them over and done with as quickly as her considerable intellect and talent let her. She wasn’t losing her mind wishing she could do something that actually required brainpower anymore - her thoughts were permanently occupied with new ways to solidify, solidify, _solidify_ each counterargument she could devise.

And before she knew it, it was time for their next co-briefing. 

Jemma was presenting a design this time, and she explained it with crisp, business-like confidence, silently revelling in the impressed look on Mace’s face.

Then Fitz got up, and launched straight into an argument she had never in a million _years_ seen coming. Who, after all, would have thought about the size of the water dispenser being an issue -

But she cut back with everything she had, backing herself up with cold, hard logic and using relevant stats to back herself up.

Fitz retreated, and she could almost see his eyes narrowing mentally.

Then he attacked again, taking yet another angle she hadn’t foreseen. 

It was uncanny, this man - he was uncanny. It was like he knew exactly how she thought, and also exactly how she _didn’t_ think - which let him spot every single flaw in her design from a mile away.

But if he could do that to her, she could do the same thing to him.

When he counter-proposed, she attacked _that_ design, cutting into it with a surprisingly vicious jab about the ridiculously small amount of dendrotoxin he was somehow postulating the biochem division had to work with.

He had to concede that point, but _she_ had to concede his point about the integrational codec she had been suggesting they put forward.

It was an impasse, and try as they might, neither of them could find a way to push past it. 

It was only a full hour into their supposed fifteen-minute briefing session that Jemma came back to reality, realising that the entire room had dropped into an awed kind of silence, looking between her and Fitz like they were two tennis champions from opposite teams.

Jemma felt rather that way herself, actually - simultaneously tense, exhausted, completely mentally strained, and absolutely _exhilarated._

She couldn’t remember the last time she had felt that _challenged_ since… well, since _ever._

And God if it wasn’t the best feeling in the entire world. 

Standing opposite her and wearing a very similar expression, Fitz gave her a slow, grudging nod, almost like that handshake between those two professional tennis players. _Well fought._

“Same time, same place next week,” she said by way of reply, gathering up her files and marching out.

She still felt… well, honestly, the right word for it was _giddy._

And brimful of rage, frustration and electric hatred, of course - but there was indisputably an element of giddiness to it too.

Being challenged like this just felt so, _so_ good. Having an _equal_ just felt so good.

Because much as she hated to admit it, that was exactly what Dr Fitz was. Her equal. 

Of course, he used it to attack her at every possible angle, every minute he possibly could… but he was still her equal.

And the design they had just worked through in that briefing, she was slowly realising, was probably the best thing this stupid company had ever seen.

Later that night, curled up with a tablet and their frantic revisions to the design, her jaw dropped all over again. 

_God._

She sought Fitz out the next day at work - she had seen a crucial error on his side, and she couldn’t _possibly_ wait a whole six more days to point it out to him.

Unfortunately for her, though, he had discovered something similar on her side, and he was _all_ too happy to go over it in detail in her empty office.

When she had to break it up to go get her lunch, she realised that she was shaking all over again. A part of it was fury, _definitely,_ yes - she just couldn’t _believe_ this man, and she couldn’t _stand_ how he kept beating her! 

Of course, she triumphed over him just as many times as he called victory over her, but the fact stood that she couldn’t _fully_ beat him. She couldn’t win.

Neither of them could.

It was the most frustrating thing in the _world_ \- but trying to beat him was the most exhilarating thing.

And Jemma thought Fitz must feel the same way, because they started meeting up more and more each day, anywhere and everywhere in the office, talking and arguing and improving, improving, _improving._ Always improving.

“Fitzsimmons are at it again,” became one of the most frequently spoken phrases in their company, and Mace’s stupid finances had never looked better thanks to their breakthroughs. But still, neither of them managed to _win._

It truly was the most infuriating thing Jemma had ever done.

And what really, _really_ wasn’t helping was that her supposedly-geniusbrain, whenever it wasn’t hard on track trying to find a flaw in Fitz’s latest argument, was managing to find the time to notice all over again how attractive he was.

Eyes that blue, a smile that distracting… it _really_ wasn’t fair.

Although she had always seen herself as more of an appreciator of symmetry in a man, there was something so _insanely_ appealing about Fitz’s cardigans.

It made his eyes stand out impossibly more, and though there was absolutely _no_ scientific explanation for it, _whatsoever,_ it made her pulse trip and stutter whenever he bent down or gesticulated particularly emphatically, allowing a tiny patch of smooth skin to peek out from underneath.

And, okay, she had seen body-building _giants_ shirtless at the gym - but this was different. A thousand times more intimate, somehow, with the soft fabric just barely showing her what she so desperately wanted to see - 

Sometimes, when she had stayed up _particularly_ late the previous night trying to find something to bring him down with, she wondered what it would be like to pull one of those cardigans right off him. She wondered what it might feel like to press her palms against that smooth, smooth skin, to pepper kisses over every tiny freckle she found, to lean against him so hard that she couldn’t tell where he began and she ended.

Sometimes, but _especially_ when they were arguing, arguing so heatedly that the space between them shrank down to millimetres, when their noses were practically brushing they were standing so close together - she wondered what it might be like to kiss him.

She could do it, too. She could push him back against that wall and finally shut up that relentlessly smart mouth of his, and find out if his tongue was just as clever in _other_ departments. She could find out just how deft and skilled his engineer’s hands were -

All of which were, of course, utterly ridiculous thoughts, and she couldn’t believe she was even thinking them.

… Alright, well, no, she could. Biologically, it made sense - it had been a while since her last good shag, and Fitz really was _incredibly_ attractive. 

It might even have worked out well, if, of course, they didn’t hate each other’s _guts._

Because they did. Hate each other, that was - Jemma didn’t think she had ever hated anyone more. She had never been this frustrated in her entire _life -_ because no matter what, she _could not win._ She couldn’t beat Fitz.

And even if she did - he’d equalise the very next day, or sooner.

And for someone as competition-oriented as Jemma, it was the world’s worst catch-22 - because she _had_ to win, she couldn’t stop trying to win because that meant _he’d_ win by omission. 

She also couldn’t win, though, not like this.

Her one consolation was that he couldn’t, either. She made _very_ sure of that. 

So, yes, while Fitz was the most maddening thing that had ever come into her life, Jemma also had to admit that she had never felt more… alive. Challenged. _Stimulated_ even. 

She couldn’t get enough of it. 

It drove her absolutely _crazy,_ but she couldn’t get enough of their forceful, ridiculously intense chase-and-pursue, shoot-and-shoot-back, circle-circle-circle, impasse-once-again game. 

//

It all came to a head at Mace’s annual Christmas party that year, when Jemma and Fitz had known each other for approximately three months, and been rivals for that very same number. 

Now, Jemma had never been expecting this party to be a _roaring_ success for her - she wasn’t the world’s biggest partygirl to start with, and anyway, Donald Bryson was going to be here. Donald Bryson… and Leopold Fitz.

Honestly, she wasn’t sure which one was worse.

Alright, no, that wasn’t quite the truth. Bryson was worse, of course - but Bryson was also _infinitely_ simpler to deal with. She didn’t have to worry about Bryson challenging her intellectually in _any_ way, and she had most certainly never been physically attracted to him. 

Fitz, on the other hand… if she wasn’t thinking about destroying him in whatever debate they were currently engaged in, she was almost certainly thinking about kissing him senseless. 

The fitted suit he was wearing tonight - blue, naturally, as _if_ the unbearably attractive blue of his eyes needed to be brought out even more - definitely wasn’t helping matters either. And though Jemma’s knee-jerk first reaction when she saw Fitz was still, _God, I hate him so much, and I want to_ destroy _him,_ it was very closely followed by _and then I’d like to destroy him the other way, too, preferably more than once._

So yeah. She had never imagined this party was going to be _amazing,_ but she also hadn’t thought it would be this bad. 

And as though that idea _somehow_ needed reinforcing, none other than Donald I’m-God’s-Gift-To-Women-How-Don’t-You-Love-Me-AlreadyBryson dropped into the barstool next to her with an overwhelming waft of men’s deodorant. 

“Doll,” he drawled, looking her up and down with appreciation. “You and I haven’t spent much quality time together lately, huh?” 

Swirling her drink, Jemma kept her eyes fixed on the bar ahead of her. “No, indeed, I’ve found myself quite busy as of late, especially since Dr Fitz’s addition to our team.” 

“Yeah, yeah, yeah, Fitzy, of course.” Bryson clapped his hands, letting out a loud, forced laugh. “Cute little rivalry you two have there, isn’t it?” 

“Thank you,” Jemma replied, keeping her gaze fixed on the bar and silently praying that he’d take the hint (not that he ever had before.) 

“That’s all there is to it, though, isn’t it?” Bryson asked, his voice surprisingly sharp for someone as generally slow-witted as him.

That was enough to get Jemma’s attention. “I _beg_ your pardon?” 

“Aw, relax, doll, I’m just cruising,” he said, waving a hand airily. “A couple of the lads seem to think that you and our Scottish friend have something else going on - ya know, other than screaming at each other with no concept of personal space.” 

Despite herself, Jemma’s cheeks heated, her mind flashing unwillingly back to all the times she and Fitz had found themselves in empty conference rooms together, both of them flushed and panting, and their faces inches apart.

“Anyway,” Bryson continued, thankfully oblivious to her thought process right then, “I just wanted to come out and prove they’re all wrong, ya know. No way would you be interested in a scrap of meat like him.” 

Jemma’s jaw _dropped._ The sheer nerve of the man! 

And as though that wasn’t _enough_ for one night, Bryson leaned forward so she could smell his beer-tainted breath, placing one meaty hand on her arm and stroking lasciviously up and down. “Not when you have me still available for you, right, doll?” 

Jemma was so utterly incredulous that she couldn’t think of a single stinging retort to respond with. Why, the sheer, impenetrable _thickness_ of this man, it was nothing short of astonishing! _How_ many times had she made it clear that she didn’t have even the slightest scrap of interest in him? 

“Doctor Bryson,” she said, removing his hand from her arm and slapping it down on the bar with a resounding _smack._ “I think you should leave.” 

“Doll,” Bryson started to protest, trying to pull her back down into her seat, but Jemma snatched her arm away. 

_“I’m not interested,”_ she said, enunciating each syllable clearly for the maximum effect. Really, only an _absolute_ nincompoop could have misunderstood her now - an absolute nincompoop, or someone who was _so_ misogynistic and self-entitled that he would honestly believe she was just playing hard-to-get.

Donald Bryson was that someone. 

“C’mon, doll, you don’t have to be coy with me,” he said in what was probably supposed to be an encouraging, seductive tone, but sounded drunken and so ridiculously self-entitled that she wanted to _slap_ him to Jemma.

And the worst part was that when she looked into his pig-like, close-set eyes, she could see that he genuinely believed every single word that had just come out of his mouth.

He _genuinely believed_ that he was so superior to her that she couldn’t _help_ but fall for him and his intoxicating power and masculinity, and in his blinding arrogance and misogyny, there was _literally nothing_ she could say to persuade him she wasn’t interested. He’d just take it as her being coy and cute. She might as well be talking to a brick wall for all she’d be able to persuade _him_ she wasn’t available. 

Then a warm pair of arms slid around her waist, and Jemma found herself tugged back ever so slightly, just enough so that she was leaning comfortably into the side of whoever had just come to her rescue. 

And the thing was… Jemma knew who it was without even seeing his face - because, much as she’d never admit it except to her dark room in the wee hours of the night, she knew what Fitz smelled like. 

They had spent enough time together (arguing, of course) in closed rooms, so it was pretty inevitable that she would get to know little details like that.

But case in point? She recognised the gentle, comforting smell of his cologne now, recognised it and instinctively relaxed back into his hold. _Better than Bryson. So, so,_ so _much better than Bryson!_

“I’m sorry for cutting in, and play along,” he murmured in her ear, his voice so low that she barely caught it, the heat of his breath causing goosebumps to rise up on her skin. 

To show that she had heard him, Jemma deliberately relaxed her body (which had tensed up as soon as he started speaking) more obviously into his hold. 

Much louder now, Fitz said with an air of affected casualness, “You still good here, love?” 

“Getting a little tired of the company,” Jemma said truthfully, turning so she was facing him side-on and giving her best attempt at an adoring smile. “I’m glad you're here.” 

Again, the truth - because she might hate Fitz as her rival, and curse his name with abandon every single day when he was ruthlessly tearing into yet another one of her projects, but he had always been incredibly well-mannered and respectful around her. She had to give him that. 

Bryson was gaping at the two of them with undisguised shock. “You two are -” 

“Absolutely,” Fitz said firmly, tightening his arm around Jemma’s waist and leaning down to kiss her on the cheek, quick and chaste, but enough to send a thrill of goosebumps prickling across her skin again. 

If he turned his head just a _little_ bit more, he’d kiss her on the lips -

Bryson, for his part, was looking like a fish whose water bowl had just been violently dumped out onto the paving. “But… but I thought… you said…” he stammered, clearly still trying and failing to put the pieces together.

“I didn’t, actually,” Jemma interjected, her voice clipped and cool. _“You_ wouldn’t let me finish. So, if you would, allow me to repeat it for you one last time, _Doctor Bryson -_ I am not, nor will I ever be, romantically interested in you. _Ever._ ” 

And while Bryson’s jaw hit the floor again, she reached calmly for Fitz’s hand, slipping her fingers into his and managing to look as though she wasn’t silently combusting inside. 

“Ready to go, darling?” she asked, using the same adoring voice she talked to her baby niece with.

“You know I can never wait to get you on your own,” Fitz said, the unexpectedly lower pitch of his voice sending shivers up and down her spine.

She forced herself to chuckle, swatting pretend-playfully at Fitz’s chest. “Oh, you.” 

And before she could get either of them into an even more potentially embarrassing situation, she tightened her grasp on his hand and tugged him away, leading him past the hordes of gawking coworkers and out into the quiet corridor behind the atrium.

Once they were out of everyone (specifically: Bryson)’s view, she dropped his hand like it had burned her (and, honestly, the jury was still out on that.)

Fitz stepped away from her just as fast, his cheeks matching hers bright red for bright red. 

The air was thick and stuffy between them, the awkwardness so palpable that you could almost cut it with a knife. 

And, God, how were they so bad at this? 

They were both people who excelled at the specific kind of intelligence required for science, and they also both excelled _spectacularly_ at arguing about science, as anyone in this office building would be able to attest. In fact, she was fairly sure they could both out-science a roomful of Nobel-prize winners without even breaking into a sweat, and as for out-arguing them, well… those poor folks would be sobbing into their trophies. 

But _this?_ Being with a Fitz completely away from science, and being with a Fitz who had just done her a ridiculously nice, gentlemanly favour - she had no _idea_ what she was supposed to do or say now that she wasn’t winding him up over his project and pitting his brilliant mind against her own.

She was pretty sure she had never felt more awkward in her life, especially when she glanced up, found Fitz doing the same, held his gaze for a fraction too long, then yanked her gaze away again, her cheeks feeling like they might actually be on fire despite the scientific impossibility of that.

Dammit, she just didn’t know what to _say_ to him if it wasn’t a direct challenge, or a blur of scientific words exchanged so fast that it took every ounce of her significant brainpower just to keep up and on track. 

Maybe she should just walk away, and pretend that this had never happened - because _clearly_ they weren’t suited to be in each other’s company if it wasn’t strictly scientific.

But… she still remembered the warmth of his arm around her waist, how it had felt like the most natural thing in the world to lean back into him and look up at him with adoring eyes.

In fact, she was only just realising that she should be _alarmed_ by how easy it had been, and by how ridiculously _comfortable_ it had felt to have his arm around her.

It didn’t make any sense whatsoever - he was her bitter rival, and she woke up in the mornings looking into her mirror and motivating herself with a “I’m going to _show_ that Leo Fitz what I can do,” speech. 

And yet, when his fingers had brushed gently across her hipbones, it had felt like the touch of a thousand stars. Little goosebumps had erupted wherever his hands had touched, even through the cottony-smooth material of her skirtdress, and her breathing had caught in her throat for no reason at all. 

It made no sense at _all,_ and yet, it was her truth.

“There’s a thin line between love and hate,” her mum had always used to say.

“Eh, maybe everyone just likes a bit of a challenge,” her dad had returned playfully one day, walking into the kitchen and bumping his wife’s shoulder. 

When her mum had given him an arch look, he had put up his hands in surrender. “What! No-one likes to be bored.” 

Her mum had rolled her eyes, but she had been smiling this affectionately-exasperated little smile, and her dad had thrown her a wink as he turned and waved her out of the kitchen.

She had always looked back on that memory with a fond exasperation of her own, but now… now she thought that she might actually understand it, and fully too, at that.

Because after all, who _did_ like to be bored? It was called _boredom_ for a reason - it was horrible! 

Maybe you _did_ need to find someone who challenged you, mind, body and soul. 

Maybe the fact that they fought, and argued, and enraged, and exhilarated each other so much was exactly what they had both _needed_ to find.

(And, of course, the physical attractiveness wasn’t a bad factor to keep in consideration, either. Those eyes, freaking _dammit -_ and she’d be a liar if she said she hadn’t checked out his arse in these suit pants at least twice tonight.) 

So, in conclusion…

(Jemma Simmons was a scientist. She knew perfectly well that no hypothesis was complete without a conclusion.)

In conclusion, she thought, she wanted to be with Fitz. Romantically.

And if the ease and natural comfort between them was any proof, they would fit _stunningly_ well together.

Good _heavens,_ this was all so absolutely perfect. 

… Now if she could just talk to Fitz, and _tell_ him what she had just realised.

“Thank you,” she blurted out before she could plan and think of something better to say. “For back there,’ she clarified in response to his raised eyebrow. “You didn’t have to, and strictly speaking I didn’t _need_ your help, but it was… very nice of you to do it.” 

“Oh, it’s no problem, _really_ \- I had the pleasure of that wanker’s company in one of our Team Engineering projects,” Fitz replied wryly, his face twisting into a grimace just at the thought. “And let me tell you, being subjected to his disgusting disgrace to the name of flirting isn’t a fate I’d wish on my worst enemy.” 

“I suppose that’s true,” Jemma said with a smile she didn’t quite feel, gesturing up and down her own body.

 _Worst enemy._ Because, yes, of course. That was how Fitz still thought of her - of _course_ it was! She hadn’t seriously been expecting half a minute of hand-holding to magically change his mind, had she? 

She was still the woman who shouted at him in every spare minute they had, who took a perverse pleasure in destroying his most carefully-prepared plans and designs and forcing him back to the drawing board to think of something better.

Yeah, _no._ He was just being his kind, gentlemanly self - because helping people out was what he _did,_ even if he did mostly hate their guts. 

(Bryson was, though, she had to concede, an extreme case to ease even the _worst_ ofrivalries for a few minutes.) 

“Thanks again,” she said, her voice brittle but still polite and pleasant as she turned away from him, silently cursing herself with every step towards the door she took. 

“Jemma, wait,” he called before she had even gotten half-way, and she froze where she stood, her heart leaping up into her throat. 

He had called her _Jemma._ Not Simmons, or Dr Simmons - _Jemma._

That _had_ to mean something, it just had to. 

“Yes, Fitz?” she asked, proud of how steady she managed to keep her voice as she turned around slowly to face him again.

He took a deep breath and blew it out slowly, then took a step forward, small and tentative. Then he took another, and another and another and another, until he was standing right in front of her, the same amount of distance between them that there was at the highest points of their arguments.

Which was to say… very, very little.

“You’re not my worst enemy,” Fitz said simply, but the look in his eyes had her completely _electrified,_ frozen in place with her lips slightly parted. “You’re more than that. You’re _so_ much more than that, Jemma.” 

There it was again, her first name. 

She swallowed hard, forcing herself not to think of tangling her fingers in that blue suit jacket of his and yanking him closer, getting rid of those last few centimetres of space between them once and for all. “What do you mean?” she asked, her voice low and breathy and, if she did say so herself, practically _screaming_ sexuality.

Fitz licked his lips, and she couldn’t help following the movement with her gaze. Oh, God, but what if she could follow that movement with her _lips_ instead of just her eyes -

“I’ll be the first to admit that I definitely did _not_ like you when we first met,” he said, his gaze still locked on hers. “I was an absolute asshole to you, and, yeah, I was exhausted and mad because I’d just been forced to settle for some sucky corporate team who didn’t know their diodes from their transistors, but that doesn’t give me the excuse to act the way I did. I was furious, and I just needed to tear into something, and I’m _really_ sorry that it happened to be you and your blueprint. You didn’t deserve it, at _all,_ and the biochem section of that project was still one of the most brilliant things I’ve ever read the specs for.” 

“I also thought that, um, you were the most beautiful woman that I’d ever laid eyes on,” he admitted, his cheeks gaining a light pink flush on top of the red which somehow managed to make him look even _more_ adorable than usual. “Which was why I hated myself and the universe so much that the _one_ time I let loose and ranted out all of my frustrations, it was to _you.”_

“I just wanted to clear up that it _wasn’t_ hate, Jemma, not even then,” he said, and the sincerity in his blue eyes as he looked down at her caught her completely by surprise. (It also caught her _heart_ completely by surprise, if the crazy beat-skipping and backflipping shenanigans it was getting up to at the moment was any indication.) 

“You got me back for that more than squarely, though,” he conceded, his eyes lighting up with a sparkle that managed to be simultaneously amused, reminiscent and still just that slightest bit frustrated. “You always have.” 

“And you’ve always one-upped me right back,” she countered, not sure why the words were leaving her suddenly so breathless. 

“We can’t win, can we?” he murmured, and there was something entirely different in the note of his voice now. His blue eyes were… darker now, almost stormy, and Jemma felt all the breath leave her lungs in a _whoosh_ as he shifted a fraction closer to her.

“Maybe we just need to learn to compromise,” she breathed, and then before she could second-guess herself, she was curling her fingers around fistfuls of his suit jacket and pulling him right down to her level.

A second before their lips touched, though, she tilted her head just slightly to the left, cutting him off. “I’m really, really glad that I’m not your worst enemy,” she said, meeting his gaze directly, “because you’re sure as hell not mine.” 

_Then_ she kissed him, finally pressing herself up against him the way she had dreamed to do for months now and carding her fingers through his short curls. 

He kissed her back immediately, gripping her waist so tightly that she gasped, a little sound which he seemed very happy to swallow with his lips, and taking the opportunity to boldly deepen their kiss and slip his tongue against hers. 

In response, she fisted her hands in his hair and pressed up higher on her toes, kissing him with everything she had, and a little more besides that.

And, honestly, she should have _known_ it was going to be like this - everything they did was a competition, after all, a constantly-challenging push and pull to see who could finally come the closest to winning. Why should kissing be any different?

It sounded like something that might not quite work on paper - challenging each other in a kiss? Really? How? - but, dear _heavens,_ it did. 

Every move she made, he echoed, and added something new on besides, something that made her press her thighs together and her toes curl in her stylish heels.

She responded in the same way, and then he did, and then her again, and back to him…

In short, it was the best damn kiss that Jemma had _ever_ had, and when she finally pulled away, her chest heaving as she gasped for breath, she couldn’t have stopped the deeply satisfied smile that curled over her lips if she had _tried._

Why the _hell_ would she try, though? This smile was living proof that her hypothesis had been exactly, _spectacularly_ right - they worked perfectly together, they really did.

Lowering one of her hands to smooth across Fitz’s now-rumpled suit jacket, Jemma tilted her head slowly to the side, letting her smile widen into a smirk as she considered her next words. “You might not be my worst enemy anymore,” she said slowly, “but you’re _crazy_ if you think I’m going to let you bullshit your way through your next project.” 

She made sure to look up and meet his gaze directly as she said, her voice as dark and filthy as she could possibly make it, “I’m going to make you work for it so fucking hard, and challenge you every single step of the way.” 

Fitz’s eyes darkened, his pupils dilating and filling up his irises until his eyes were almost completely black - a stormy, electric blue-black, _just_ for her. 

Letting go of her waist, he grabbed one of her hands and pulled her roughly into the nearest empty room - which, Jemma noticed with a quirk of amusement, turned out to be conference conference room five.

Well, _that_ felt like fate. 

She forgot all such ironically romantic notions when he spun her around and pushed her against the door, though, bracing his arms on either side of her head and looking down at her with those dark, dark blue eyes.

“You will, and so will I,” he said, and she knew it was a promise. “And I look forward to it. But right now?” 

He unashamedly _smirked_ at her, dropping one of his hands to tug at the zipper of the ever-so-stylish coatdress she had worn for the evening. “I think I know a way we can both win.” 

_**The End.** _


End file.
